1. Field of the Invention
The present invention relates to accessing to a hybrid network, and more particularly, to a method for accessing multiple networks of a hybrid network with reduced power consumption, which reduces the time consumption of a gateway node in the idle state for simultaneously sensing two networks while ensuring different network signals from the hybrid network are simultaneously received, so that power consumption per unit time of the gateway node is reduced, and the standby or serving time of the gateway node is increased, and gateway apparatus, wireless terminal and communication system thereof.
2. Description of the Prior Art
With the popularity of wireless portable terminals and the development of communication services in various fields, the future mobile communication system is required to perform communication in a “ubiquitous” manner, that is, an effective wireless transmission should be ensured anytime and anywhere. However, in the conventional cellular network, the communications between mobile terminals must be transferred by aid of base stations and (or) mobile switches, which makes the communication manner be limited by various factors such as geographical regions. For this, the wireless distributed network independent from fixed network infrastructure is proposed as a flexible wireless access manner, is considered as a supplement to and as a development of the fixed networks, and thus makes the “ubiquitous” communication manner possible. In such an extended network environment, research about communication techniques will not be limited only to any individual network, and the coexistence between the hybrid networks and the access methods of the wireless terminal in the hybrid network also become one of the most concerned subjects.
The appearance of the wireless distributed networks, such as Wireless Local Area Network (WLAN), Ad hoc and Bluetooth, makes the constitution of a hybrid network more flexible. On the basis of the architecture of a wide area cellular network, these distributed networks provide broader network coverage, increase the system capacity, and especially solve the wireless communication problems by supporting direct communications among nodes in some scenarios, such as the hotspot areas with heavy communication loads, blind-spot areas in which a central controller of the wide area cellular network cannot be directly reached, and a case where a wireless terminal has insufficient power to maintain a long-distance communication. However, since different networks employ different communication protocols, the conventional wireless terminal or node can only support transmissions in one network. For this, how to support simultaneous communication with multiple networks in the hybrid network without influences on the transmission performance of each network is a problem to be solved when extending the medium access method to the hybrid networks.
The most direct method for accessing multiple networks of a hybrid network is to employ a dual-mode wireless terminal. The dual-mode wireless terminal has a function of supporting two communication protocols, which can flexibly select a network to be accessed according to network conditions. For example, Reference 1 (CN 1604686, Apparatus and Method for Selecting Access Network in Hybrid System, Sep. 27, 2004, Samsung Electronics Co., Ltd.) proposes that a wireless terminal determines the network to be connected according to a predetermined priority list, and when that network fails to be connected, attempts to access a network with a next lower priority.
Similarly, Reference 2 (GB 2269723) proposes a mobile wireless phone supporting both cellular and local cordless system. Firstly, a call is routed to the cordless phone through the cordless network. Only when the position of the mobile phone cannot be determined, the cellular and the cordless system are then connected through the cellular network. Although the wireless terminals in the above systems support transmissions in more than one network, they only maintain the connection with one network at any time and thus cannot receive signals from another network. For example, in Reference 1, once the terminal can successfully access to the network with the highest priority, it will maintain the connection with the network without considering signals from other networks, so that calls from other networks cannot reach the wireless terminal. Therefore, a true dual-mode wireless terminal needs to have a capability of simultaneously receiving signals from two networks. Reference 3 (http://china.nikkeibp.co.jp/china/news/tel/tel200407190109.html) discloses that FOMA/WLAN N900iL manufactured by NEC Corporation of Japan can support a wireless terminal simultaneously operating on hybrid networks. The user may switch the operation mode among single FOMA network, single wireless local area network and dual-mode. As shown in FIG. 1, FOMA provides wide area coverage based on WCDMA technology. WLAN fulfills requirements of hotspot areas or high-speed transmissions through an Access Point (AP). The wireless terminal may simultaneously receive signals from two networks by operating in a dual-mode. However, since the terminal in the dual-mode needs to detect signals of two networks simultaneously, it requires large power consumption and thus the standby time of the terminal is shortened. For example, N900iL may standby 280 hours when operating in single FOMA network, and may standby up to 230 hours in single wireless local area network. If the dual-mode is enabled, the standby time is only 150 hours. Therefore, it is necessary to reduce the power consumption of the terminal as much as possible in order to extend the serving time while ensuring successful signals reception from two networks.
Though the dual-mode wireless terminal may support communication with multiple networks, there are a number of conventional nodes only supporting one communication protocol in the hybrid network. Considering backward compatibility, how to make these single-mode nodes be better served is also a problem to be solved by the medium access control. Relay is a common access manner, that is, a dual-mode terminal is used as a relay node. When some conventional single-mode nodes cannot be connected to the systems in which they have registered, the communication may be achieved by first connecting to a surrounding dual-mode terminal and then being forwarded by the dual-mode terminal to another network. In this way, some nodes that would not perform communication initially can obtain a better quality of service and the flexibility of network extension is enhanced by the dual-mode terminal. Reference 4 (H. Wu, C. Qiao, S. De, and O. Tonguz, Integrated cellular and ad hoc relaying systems: iCAR, IEEE Journal on Selected Areas in Communications, vol. 19, No. 10, October 2001) proposes that the congestion problem of the wide area cellular network can be solved by using Ad hoc Relaying Stations (ARS). When resources in a cell are not enough to admit more calls, the calls may be transferred to adjacent cells through the surrounding ARS in order to mitigate the system congestion due to imbalanced service distribution. However, this method requires the establishment of the special ARS in the system which brings a large system overhead and influences on the system flexibility. Reference 5 (Y. D. Yin, and Y. C. Hsu, Multihop Cellular: A New Architecture for Wireless Communications, IEEE INFOCOM, 2000) proposes that when the source and the destination nodes are located in one cell, the system capacity is improved by a method in which the communication is achieved by multiple relay connections between nodes in the cell. However, these methods all assume that all nodes in the system have the capability of supporting communications in two networks, and thus cannot support the conventional single-mode terminal in the hybrid systems, and the power consumption problem of the nodes in the system is not considered. Therefore, the present invention relates to a hybrid network which may connect with a wide area cellular network through a relay node (a gateway node), which while ensuring network connectivity as much as possible, reduces power consumption of the relay node in idle state due to simultaneously sensing signals from two networks, in order to increase the standby or serving time thereof.